The present disclosure relates to a polyphenylene ether composition with improved die lip buildup performance. In particular, the present disclosure relates to a polyphenylene ether composition wherein the levels of die lip buildup are substantially reduced. The present disclosure also relates to a process for the preparation of a polyphenylene ether composition with improved die lip buildup performance.
Polyphenylene ether (PPE) resin compositions are useful in several industries depending on the intrinsic viscosity thereof such as adhesives, sealants, gels, automotives, cabling, electrical applications, aerospace, sporting equipment, electrical laminates, and IC encapsulation materials. Polyphenylene ether resins are also useful as additives for various thermoplastic and thermoset materials. Polyphenylene ether resins can also be used to improve the heat performance, flame retardant properties, decrease of some electrical properties, decrease in moisture absorption, increased creep resistance, thermal expansion reduction, and the like in several applications. The physical, electrical and chemical properties of polyphenylene ether resin compositions make them ideal for a wide variety of industrial applications. Polyphenylene ether resin compositions can be manufactured by film/sheet extrusion, blow molding, film blowing, extrusion coating, and fiber spinning. However, such manufacturing processes suffer from a significant disadvantage in the formation of a die lip during the process. Die lip buildup is a phenomenon in which material accumulates at the open faces of the die during extrusion. Excessive die lip buildup diminishes both the aesthetic quality and engineering properties of the product, and it can force a shut down of the processing operation resulting in a huge loss in productivity. It is often necessary to shut down the process in order to enable cleaning of the die to ensure that the product formed is uniform and does not suffer from any surface defects occasioned due to the formation of the die lip buildup. This results in a downtime in the manufacturing process and increased costs.
The formation of die lip buildup can, for example, affect the surface qualities of the product being manufactured due to the formation of melt fractures and deformities. Die lip build up is a problem faced in several polymer extrusion processes. However, this problem is particularly significant in the extrusion of polyphenylene ether resin compositions. Several methods have been proposed to overcome this problem including mechanical alterations to the die shape and size.
For example, U.S. Pat. No. 5,435,708 teaches a melt blowing die head with opposing die lips mounted on lip guides pivotally connected to respective set back bars. To facilitate cleaning of the die, the lips are swung away from the spinneret on the respective lip guides. While this results in reduced down time in the maintenance of the die, it does not avoid the problem of stopping the manufacturing process, and does not facilitate cleaning or maintenance during manufacturing operation.
U.S. Pat. No. 6,245,271 teaches a process for die extrusion of melted polymers that reduces die lip buildup. The process comprises providing at least two separate sources of compositions containing the molten thermoplastic polymer, then combining the compositions within a die into layers where one layer is exposed and is of a specified thickness (not more than 15% thickness of the two layers), and then extruding the combined layers. The die lips have a specific radius of curvature in the range of from 0.5 mil to 3 mils. This disclosure focuses on the alteration of the die lip and the formation of two distinct layers. The patent does not mention any other factor as being important for avoiding die lip buildup. A disadvantage of this patent is its limited applicability to the manufacture of fibers for applications such as diapers and incontinence garments. It does not solve the problem of different sized die lips. Also, on the face of it, this appears to be incapable of being performed where the die lips are of dimensions beyond those specified dimensions. This disclosure is also silent of its applicability in respect of polyphenylene ether resin compositions.
WO 02/28971 teaches a polyphenylene based composite resin composition for injection molding an IC tray, wherein the composition comprises polyphenylene oxide or polyphenylene ether in an amount of 20 to 98% by weight of the total composition, one or more resins are included which are selected from the group consisting of polystyrene, polyphenylene sulfide, polyetheramide, polycarbonate, and polyethylene including high density polyethylene, low density polyethylene, linear low density polyethylene, and very low density polyethylene in an amount of 1 to 40% by weight of the total composition and inorganic and glass fiber as fillers in an amount of 1 to 40% by weight of the total composition. While it is claimed that this composition has enhanced mechanical strength, dimensional stability, low linear fever expansion coefficient, and good outlook of the product, there is no disclosure or teaching therein of any reduction in die lip formation.
It is therefore desirable to provide a method by which die lip buildup in polyphenylene ether resin compositions can be avoided or minimized, thereby providing significant advantages in the manufacture of PPE resin based articles such as reduction in down time.